Residual current safety switch

ABSTRACT

A residual current safety switch has a residual current transformer (3) connected to an evaluation circuit (5) that controls an electromagnetic trigger device (K1) for actuating switching contacts (1, 2). An overvoltage protection circuit (V1), for example designed as a voltage-dependent resistor, is provided. The evaluation circuit (5) and/or the overvoltage protection circuit (V1) are/is connected to terminals that supply them with voltage when the switching contacts (1, 2) are closed through lines (7, 8), with one of the lines extending through the residual current transformer (3) and the other not. The supply current of the electronic components and/or the current that flows through the overvoltage protection circuit (V1) is lower than the triggering current when the nominal voltage is applied.

BACKGROUND OF THE INVENTION

The invention refers to a residual current safety switch of a typeincluding a residual current transformer and an evaluation circuitconnected therewith and controlling an electromagnetic trigger devicefor actuation of switching contacts, and further including anovervoltage protection circuit, e.g. in form of a voltage-dependentresistor.

Conventional residual current safety switches of this type (hereinaftercalled short "DI-switch") effect the voltage supply of the electroniccomponents via an auxiliary contact connected to a power line eitherbefore the residual current transformer or after the residual currenttransformer. This solution has the drawback that the electroniccomponents as well as the pertaining overvoltage protection remainunprotected, and excessive power supply may lead to a defect of thisprotection, or in case of outage of voltage supply to the electroniccomponents, without any capability to recognize such a defect fromoutside.

SUMMARY OF THE INVENTION

It is the object of the invention to eliminate these drawbacks and toprovide a DI-switch of the afore-described type, which protects theinstalled overvoltage protection as well as the voltage supply circuitof the electronic components.

In accordance with the invention, this is attained with a residualcurrent safety switch of the afore-stated type by connecting anevaluation switch and/or the overvoltage protection circuit to poweroutlets for supply of voltage when the switching contacts are closedthrough lines, with one line extending through the residual currenttransformer and the other line being guided outside the residual currenttransformer, wherein the supply current of the electronic componentsand/or the current that flows through the overvoltage protection circuitis lower than the triggering current when the nominal voltage isapplied.

Through these measures, the occurrence of static overvoltages, ofexcessive power supply, or a defect of the voltage supply of theelectronic components results in an activation of the trigger device.Thus, the residual current safety switch is capable to separate itselffrom the power supply at particular defects or overloads of theelectronic components to eliminate any risk that the malfunction of theswitch remains unnoticeable under certain conditions.

According to another feature of the present invention, the overvoltageprotection circuit is connected parallel to the evaluation circuit, andthe trigger device is connected in series to this parallel connection.This is advantageous as an adjustment of the sensitivity of theovervoltage protection over a wide range is effected, withoutsignificantly influencing the evaluation circuit, whereby a remainingimpact can be taken into account during configuration and dimensioningof the evaluation circuit.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described in more detail with reference to thedrawings, with FIGS. 1, 2, 3 schematically illustrating differentembodiments of a DI-switch according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The DI-switch according to FIG. 1 is connected by the fixed conductorsof both its switching contacts 1, 2 to power outlets L, N. Positioneddownstream of these switching contacts 1, 2 is a residual currenttransformer 3 which has a secondary winding 4 connected to theevaluation circuit 5 that evaluates an encountered secondary currentcaused by residual current.

The evaluation circuit 5 is connected to an electromagnetic triggerdevice K1 for controlling the switching contacts 1, 2 and an auxiliarycontact 6 which separates the electronic components from the poweroutlet independently from the power supply end or consumer end of theDI-switch.

The voltage supply of the evaluation circuit 5 is effected via theelectromagnetic trigger device K1 as well as via the lines 7, 8 and thepreceding auxiliary contact 6, with one of both lines 7 or 8 (line 8 inthe attached Figure) extending through the residual current transformer3 and tapping the voltage only behind the differential currenttransformer 3, and the second line (line 7 in the attached Figure) notextending through the transformer and tapping the voltage already beforethe residual current transformer.

Further connected in parallel relationship to the evaluation circuit isan overvoltage protection element V1.

The voltage-dependent resistor V1 is so dimensioned that the currentflowing through the voltage-dependent resistant V1 at nominal voltage orat elevated voltage only within a tolerable degree is smaller than theresidual current required for a triggering.

When encountering an overvoltage or a defect in the voltage supply ofthe evaluation circuit, a respective residual current flows through thetransformer 3 and is recognized as faulty current so that the triggerdevice K1 is activated by the evaluation circuit 5 when a particularpreset value is exceeded.

As a result, also the supply of the evaluation circuit 5 and thus of theovervoltage protection circuit formed by the overvoltage protectionelement V1 is interrupted, to thereby eliminate a damage to theDI-switch and a threat to the installation connected.

A resistor RT switched in series with a test key T is further disposedin a line 9 which connects the lines N and L when the switching contacts1,2 and thus the auxiliary contact 6 are closed. By pressing this key T,a residual current flows across the resistor RT and via the lineextending externally of the residual current transformer 3 and is ofsuch magnitude as to enable an activation of the trigger device K1.

The embodiment according to FIG. 2 differs from the one according toFIG. 1 in that the voltage-dependent resistor V1 is not connected inparallel to the outputs of the evaluation circuit 5; Rather, it isconnected via the electromagnetic trigger device K1 with the one liveterminal L and via the line 8, which is guided through the residualcurrent transformer 3, with the other live terminal N. The evaluationcircuit 5 is fed independently from the line 8 which is guided throughthe residual current transformer 3.

The conditions in the embodiment according to FIG. 3 are exactlyreversed as in FIG. 2 by feeding the evaluation circuit 5 only via theline 8 which is guided through the residual current transformer 3, butnot the voltage-dependent resistor V1.

The embodiments according to FIGS. 1 to 3 differ thus from each other insuch a manner that upon closing of both switching contacts 1, 2, theevaluation circuit 5 as well as the overvoltage protection circuit V1are connected via the lines 7, 8 with live terminals in case of FIG. 1,while in accordance with FIG. 2 this is true only with regard to theovervoltage protection switch V1, and in accordance with FIG. 3 onlywith regard to the evaluation circuit 5.

What is claimed is:
 1. A residual current safety switch, comprising:a residual current transformer (3); an evaluation circuit (5) connected to the transformer and controlling an electromagnetic trigger device (K1) for actuation of switching contacts (1, 2); and an overvoltage protection circuit (V1), wherein at least one element selected from the group consisting of the evaluation circuit (5) and the overvoltage protection circuit (V1) is connected to power outlets (L, N) when the switching contacts (1, 2) are closed for providing a voltage supply, with the connection between the at least one element and the power outlets being effected by lines (7, 8), with one line extending through the residual current transformer (3) and the other line being guided outside the residual current transformer (3), wherein the supply current and/or the current that flows through the overvoltage protection circuit (V1) is lower than the triggering current when the nominal voltage is applied.
 2. The residual current safety switch of claim 1 wherein the overvoltage protection circuit (V1) is coupled to the evaluation circuit (5) by a parallel connection, and the trigger device (K1) is connected in series to the parallel connection. 